1. Field of the Invention
The present invention relates to a three-terminal dip type capacitor.
2. Description of the Related Art
In general, a three-terminal dip type capacitor (hereinafter referred to as "three terminal capacitor") has three lead terminals 1, 2aL and 2aR extending from an armor resin 6 in alignment as shown in FIG. 12. Among these three terminals, the outer two lead terminals 2aR and 2aL are commonly connected to one of charge accumulating opposing electrodes of a capacitor element within the armor resin 6, and thus are constructed to have equal potential to each other. The central terminal 1 is connected to the other of the opposing electrodes with respect to the outer two terminals 2aR and 2aL. Accordingly, between the central terminal and the left and right terminals respective capacities are generated. With such terminal arrangement, when such a capacitor is installed on a printed circuit board, for example, so-called reverse installation, wherein the orientation of the capacitor is reversed with respect to the predetermined orientation, which results in reversal of polarity of charge voltage, may not be caused. Therefore, such terminal arrangement is quite useful for the case of polarized capacitor, such as a solid state electrolytic capacitor.
Hereinafter, discussion will be given for the construction of the conventional three-terminal capacitor. FIG. 1 shows an external view of an example of a cylindrical capacitor element, for which a process of production of the conventional three-terminal capacitor has been disclosed in Japanese Unexamined Patent Publication (Kokai) No. Showa 62-150816 (Patent Application No. Showa 60-294362) is applied. Hereinafter, the three-terminal capacitor fabricated through this process will be referred to as a capacitor of the prior art 1. It should be noted that FIG. 1 is illustrated without the armor resin for simplification of the following discussion. Referring tso FIG. 1, the capacitor includes a lead terminal 2c bent into essentially into a channel-shaped configuration. A solid state electrolytic capacitor element 3 (hereinafter referred to as "capacitor element") formed of a valve function metal, such as tantalum and the like, is disposed between both leg portions of the lead terminal 2c. Both leg portions and upper bridging portion are fixedly bonded onto the side surface and upper surface of the capacitor element by a conductive bond 5. For a tantalum wire 4 extending vertically from the center of the lower surface of the capacitor element 3 perpendicular to the lower surface, a lead terminal 1 is welded. In the solid state electrolytic capacitor, the periphery of the capacitor element 3 normally becomes cathode the side, with lead terminals 2c serving as terminals, and the tantalum wire at the central portion of the lower end of the capacitor element 3 becomes the anode, with the lead terminal 1 becomes serving as an anode lead terminal.
In such a three-terminal capacitor, it is inherently required to connect at least one of the peripheral surfaces or upper and lower end surfaces to a cathode lead terminal 2c. However, in the capacitor of the prior art 1 set forth above, a problem is encountered in the reliability of connection between the capacitor element 3 and the cathode lead terminal 2c. Namely, when a vibration or an impact is applied to the capacitor element in the axial direction, the connecting portion of the capacitor element 3 and the cathode lead wire 2c can be peeled off.
In order to improve the reliability of connecting in the three-terminal capacitor, there has been proposed a capacitor (hereinafter referred to as "capacitor of the prior art 2") having the construction as illustrated in FIG. 2. It should be noted that the conductive bond for connecting the capacitor element 3 and the cathode lead terminal 2dL,2dR and the armor resin are neglected to maintaining the following discussion simple enough for facilitating understanding. Referring to FIG. 2, in the shown capacitor, the cathode lead terminal is separated into a lead terminal 2dL supporting the capacitor element 3 at the left side and a lead terminal 2dR opposing to the lead terminal 2dL and supporting the capacitor element at the right side. Each of the cathode lead terminals 2dL and 2dR includes an arc-shaped portion extending in an arc-shaped configuration along the circumferential surface of the capacitor element 3, and a straight portion extending perpendicularly (in the axial direction of the capacitor element 3) to the arc-shaped portion. With respect to this capacitor, considering the construction on the plane perpendicular to the anode lead terminal 1 and including the arc-shaped portions of the lead terminals 2dL and 2dR, the arc-shaped portion uniformly supports the capacitor element 3 in substantially all directions. Accordingly, even when a vibration or an impact is exerted on the capacitor from any horizontal (perpendicular to the axis of the capacitor element 3) direction, connection between the capacitor element 3 and the cathode lead terminals 2dL and 2dR may not be damaged.
As set forth above, the capacitor of the prior art 2 as illustrated in FIG. 2 has the advantage for of higher reliability of connection between the capacitor element and the cathode lead terminal, in comparison with the capacitor of the prior art 1 illustrated in FIG. 1. However, it has the problem the increasing of production cost and, thus, of being expensive. The reason will be below.
FIGS. 3 to 6 show an external view of a production process of the capacitor of the prior art 2. First, a right cathode lead terminal 2dR is mounted on strip 5dR, and the anode lead terminal 1, connected to capacitor element 3, is mounted to strip 53. Then, positioning is performed as illustrated by the arrow of the broken line so that two strips 5dR and 53 are arranged in an overlapping manner. At this time, a distance L.sub.dR between the cathode lead terminal 2dR and the anode lead terminal 1 of the capacitor element 3 must be set to be greater than an original distance (namely, substantially equal to the radius of the capacitor element) at completion of production of the capacitor. It should be noted that, in the practical production process, while a plurality of cathode lead terminals 2dR and the capacitor elements 3 are mounted on the strip 5dR and the strip 53, only one of each is shown in FIG. 3 for simplification of the disclosure.
Next, as shown by the solid line arrow in FIG. 4, the overlapped strip 53 is shifted toward the right on the plane of FIG. 4 to engage the capacitor element 3 and the right side cathode lead terminal 2dR.
Subsequently, as shown in FIG. 5, the left side cathode lead terminal 2dL mounted only to the strip 5dL is prepared. Then, the strip 53 is positioned as shown by the broken line in FIG. 5. The strip 5dL is then overlapped to the strips 5dR and 53, which are already obtained through the process step of FIG. 4. At this time, a distance L.sub.dL between the cathode lead terminal 2dL and the anode lead terminal 1 of the capacitor element 3 is set to be greater than the original distance at completion of production.
Thereafter, as shown by the arrow in solid line, the strip 5dL is shifted toward the right in FIG. 6 to engage the cathode lead terminal 2dL to the capacitor element 3. Furthermore, the peripheral surfaces of the cathode lead terminals 2dR and 2dL and the capacitor element 3 are fixedly bonded by way of application of a conductive bond, dipped into molten solder liquid, and so forth.
Finally, by way of dipping method, the armor resin is applied. Thereafter, the lead terminals are cut off the strip to complete the capacitor of the prior 2 as illustrated in FIG. 2. It should be noted that, in FIG. 2, as set forth, the conductive bond and the armor resin have not been shown to simplify the disclosure.
As can be clear from the foregoing discussion of the production process, in the capacitor of the prior art 2, after overlapping the strips, the strips must be shifted twice. In contrast, the capacitor of the prior art 1, upon assembling the cathode lead terminal and the capacitor element, as disclosed in the publication, only requires placing the channel-shaped cathode lead terminal on the strip, on which the capacitor element is mounted an overlapping manner. The later method does not require lateral sliding of the strips.
Thus, in order to fabricate the capacitor of the prior art 2, after overlapping the strips, at least two extra steps are required for laterally shifting the strips to require higher production cost.